The attacker has been named as Salman Abedi and a 23-year-old man has also been arrested in connection with the atrocity.

Speaking outside Downing Street after chairing a meeting of the Government’s Cobra emergency committee, May said the perpetrator had chosen the time and place of his attack deliberately to cause “maximum carnage and to kill and injure indiscriminately”.

May, who later flew to Manchester to speak to police chiefs, paid tribute to emergency workers and members of the public who rushed to help.

People gather ahead of a vigil in Albert Square, Manchester Martin Rickett/PA Wire

The PM said: “It is now beyond doubt that the people of Manchester and of this country have fallen victim to a callous terrorist attack, an attack that targeted some of the youngest people in our society with cold calculation.

“This was among the worst terrorist incidents we have ever experienced in the United Kingdom, and, although it was not the first time Manchester has suffered in this way, it is the worst attack the city has experienced and the worst ever to hit the north of England.

“We now know that a single terrorist detonated his improvised explosive device near one of the exits of the venue, deliberately choosing the time and place to cause maximum carnage and to kill and injure indiscriminately.

“All acts of terrorism are cowardly attacks on innocent people, but this attack stands out for its appalling, sickening cowardice, deliberately targeting innocent defenceless children and young people who should have been enjoying one of the most memorable nights of their lives.”

An artist writes a message in St Ann's Square, Manchester, the day after a suicide bomber killed 22 people, including children, as an explosion tore through fans leaving a pop concert in Manchester. PRESS ASSOCIATION Photo. Picture date: Tuesday May 23, 2017. See PA story POLICE Explosion. Photo credit should read: Martin Rickett/PA Wire

The Prime Minister said the official threat level remains at severe - meaning an attack is highly likely - but this would continue to be assessed.

Police were called to reports of an explosion at the Manchester Arena at 10.33pm on Monday, shortly after the end of the performance.

The massive blast sparked panic as crowds rushed to exit the venue, which has a capacity of 21,000.

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